1. Field of the Invention
The present invention relates to an origin calibrating method for articulated robot arms, particularly, a method for calibrating an angle deviation for arms in zero position thereof.
2. Related Background Art
Japanese Patent Application Laid-Open Nos. 63-101907 and 1-193190 and Japanese Utility Model Application Laid-Open No. 1-143377 are known as examples in the prior art of a method for calibrating an arm origin for articulated robots requiring absolute accuracy.
According to Japanese Patent Application Laid-Open No. 63-101907, arms to be calibrated are positioned at three known points, and data obtained thereby is operated on for obtaining an angle deviation for robot arms.
According to Japanese Patent Application Laid-Open No. 1-193190, a certain point is taught to a robot by means of a right-hand system and a left-hand system for positioning at the point, and the internal data of a robot thereat is operated on for obtaining an angle deviation for arms.
On the other hand, Japanese Utility Model Application Laid-Open No. 1-143377 proposes a mechanical calibrating method for an arm origin. In other words, mounted on the arm side are a jig main body for origin calibration, a center shaft, a zero master, and distance detectors for the jig main body. An arm position is adjusted such that there is no difference in output between two distance detectors with respect to the position of the center shaft.
However, according to the examples of the prior art, particularly, the methods proposed by Japanese Patent Application Laid-Open Nos. 63-101907 and 1-193190, since a robot is positioned in a predetermined position for calibration, a pin of a predetermined shape mounted at an arm tip is inserted into a predetermined engaging hole. As a result, involved is a problem that this positioning work takes time. Moreover, since a positioning accuracy is determined by this engagement, an allowance for this engagement needs to be made smaller, causing the positioning work to become more difficult.
Also, according to the method using a calibrating jig as proposed by Japanese Utility Model 25, Application Laid-Open No. 1-143377, a high-precision jig, a shaft, a zero master, etc. are needed, and moreover, a plurality of engaging holes of good accuracy are needed for accurately fixing such devices on arms, causing an increase in robot cost.